As a result of past intensive studies, many compounds having an antitumor activity have been put into practical use. Anticancer agents that are currently used in clinical practice show temporary regression and disappearance of cancer, but they also have non-selective toxicity to normal cells, causing serious adverse effects; thus, use thereof is restricted. Further, inherently resistant cancer against which an anticancer agent is not effective and acquisition of resistance to an anticancer drug which is found mainly in cases of recurrence have also been clinical problems. Under such circumstances, creation of a new antitumor agent has still been desired.
It is known that many actinomycetes are capable of producing an antibiotic. Hence, the search for a novel compound derived from an actinomycete has widely been conducted.